The erythemal exposure due to filtered ultraviolet radiation
has been evaluated with a dosimetric spectrum evaluator in a
glass enclosure to simulate a sun-room with glass roof and walls,
in a greenhouse and in a small and large car. The ratio expressed
as a percent of the erythemal irradiances to the shoulder of a
person in an upright position inside each of the environments to
those measured outside the enclosures were 5 to 7%, 1%, 1.2% and
0.7%. The average of the erythemal exposures to the facial sites
over a six hour period were 0.05 MED and 0.02 MED for the small
and large car respectively. Although the exposure was a fraction
of an MED, the cumulative exposure received by humans in the
above enclosures in a fortnight is of the same order of magnitude
as that received during periodic leisure activities in the
outdoor environment.

Introduction

Approximately 800 Australians die annually from melanoma and
200 annually from non-melanoma skin cancer (NMSC) (Foot et al., 1993). Skin cancer is
estimated to cost the Australian community an estimated $400
million per year (Girgis et al., 1994).
Additionally, there is the human suffering costs. Queensland,
Australia due to its low latitudes and relatively clear skies has
high levels of ambient solar UV radiation (280-400 nm) and has
the highest incidence rates of NMSC and cutaneous malignant
melanoma in t he world (Lowe et al.,
1993). Ultraviolet radiation exposure has a causative role in
human skin cancer (Longstreth et
al., 1995).

The damaging effect of UV radiation on human skin can be
expressed employing the human erythemal action spectrum in Figure
1 (CIE, 1987) to calculate the
biologically effective UV irradiance (UVBE) as follows:
where S()
is the source spectrum and A() is the erythemal action spectrum. Figure
1 shows the erythemal response of human skin (CIE, 1987) with the value of the
sensitivity dropping by about 3 decades for the UVB waveband
(290-320 nm). In the UVA waveband (320- 400 nm), the value of the
action spectrum varies from 10-3 to 104.
Thus the damage caused by the UVB band of radiation is far more
important than that caused by the UVA band.

Transparent screens such as glass and automobile windscreens
and window glass act as a barrier to some of the shorter solar
ultraviolet radiation wavelengths (Gies
et al., 1992,Parisi and Wong,
1997) and as a result can provide a degree of protection to
humans. Although filtered solar ultraviolet radiation is
predominantly in the UVA band, its harmful effect is not to be
under-estimated because of the high level of irradiance. Recent
research (Lavker et al., 1995) has
shown that repetitive exposures to relatively low UVBE due to UVA
wavelengths has a cumulative effect and can produce skin
alterations indicative of early tissue damage. Sutherland et al. (1991) found
that UVA exposure can induce pyrimidine dimers and as a result
can cause DNA damage in human skin.

Human exposure to solar UVB and ambient solar UVB have been
measured by a number of authors using polysulphone dosimeters (Wong et al., 1996,Gies et al., 1995) and Robertson-Berger
meters (Scotto et al., 1988).
These detectors do not have a significant response in the UVA
waveband (Figure 1). This paper presents a recently developed
method based on a dosimetric technique of evaluating the UVA
spectrum to allow calculation of the biologically effective UV
for the particular action spectrum. Development and testing of
the method has been described elsewhere (Parisi et al., 1996, Parisi et al., 1997, Wong and Parisi, 1996). The erythemal
UV due to filtered solar UV radiation in a glass enclosure to
simulate a sun-room with glass roof and walls, in a greenhouse
and in two cars will be compared.

A recently developed UV spectrum evaluator, (Wong and Parisi, 1996) with four types
of UV sensitive dosimeter films was employed for evaluation of
the filtered solar ultraviolet spectrum. The dosimeter materials
employed in the spectrum evaluator are polysulphone, nalidixic
acid (NDA), 8-methoxypsoralen (8MOP) and phenothiazine (Parisi et al., 1997). A piece of the
material of approximately 1 cm2 was placed over a 0.6
cm diameter hole in a holder with an overall size of 3 cm x 3 cm
in the form of a film badge. The materials change their optical
absorbance after exposure to ultraviolet radiation. This was
determined for each material by measuring the absorbance at 330
nm for both polysulphone and NDA, 305 nm for 8MOP and 280 nm for
phenothiazine before and after exposure in a spectrophotometer
(Shimadzu Co., Kyoto, Japan). The post-exposure absorbance was
measured as soon as practical following the exposure.

Each type of film is responsive to different UV wavebands (Wong and Parisi, 1996). The result of
the change of absorbance in these films caused by the exposure to
solar radiation was used to evaluate the UV source spectral
irradiance applied to the device (Parisi
et al., 1997). The spectral irradiance was used to calculate
the erythemally effective irradiance using Equation (1). The
change in absorbance in the dosimeter materials is a result of
the total integrated exposure over the period. As a result, the
spectrum evaluated is the time averaged spectrum over the period.
Unlike the popular UV dosimeter such as polysulphone, this device
has a significant sensitivity over the entire range of UV
wavelengths. For measurements of glass filtered solar UV
radiation, a horizontal spectrum evaluator requires approximately
20 minutes exposure in the midday sun (ambient irradiance 7 to 24
Wcm2)
to produce a measurable change in the detectors.

Filtered Solar UV

The filtered solar UV irradiances were measured in Toowoomba,
(27.5o S latitude) Australia between 4 September, 1996
and 25 August, 1997. The filtered UV exposures to a horizontal
plane and to four vertical planes orientated to each of 0o,
90o, 180o and 270o of azimuth
angle from north in a glass enclosure to simulate a sun-room with
glass roof and walls and in a greenhouse were measured using UV
spectrum evaluators. Three sites at the eastern side, centre and
western side of the greenhouse were simultaneously measured. A
car from the small class and a car from the large family class
were employed with the spectrum evaluators deployed at body sites
over a manikin in each of the drivers seats. Both cars had the
windows fully wound up with the manufacturer's tint on the
windows of the large car and no tint on the small car windows.

For the glass enclosure the spectrum was evaluated at three
exposure times, namely, 9.00 to 9.20 Australian Eastern Standard
Time (EST), 11.50 to 12.10 EST and 14.40 to 15.00 EST. The
exposure times for the greenhouse were 9.00 to 10.00 EST, 11.30
to 12.30 EST and 14.00 to 15.00 EST and for the cars they were
9.00 to 12.00 EST and 12.00 to 15.00 EST. In each case, the
length of the exposure times was chosen as a compromise between a
sufficient exposure to produce a measurable change in absorbance
in each of the four materials and not too long so that there was
not a saturation of the response in any of the dosimeter
materials. The unfiltered erythemal UV on a horizontal plane was
measured outside each enclosure at the start, middle and end of
the six hour period with a meter (Model 3D V2.0, Solar Light Co.,
Philadelphia, USA).

Typical Scenarios

The erythemal exposure due to filtered solar UV to humans in
three hypothetical scenarios at the latitude of the measurements
in this paper were estimated. It was assumed that no personal sun
protection measures such as hats or sunscreens were implemented.
It was also assumed that the daily exposure remained
approximately unchanged over the period of a fortnight. The
scenarios considered were:

A. The erythemal UV exposure to the upper arm of a farmer
in the glass cabin of his tractor planting, cultivating
or harvesting the winter crop for 6 hr/day for 12 days
per fortnight compared to the erythemal UV exposure to
the shoulder of a spectator in the open at a winter sport
such as football for 1 hr per fortnight.

B. The erythemal UV to the shoulder of a worker in a
greenhouse in summer for 6 hr/day for 12 days per
fortnight compared to a visit to the beach in summer of 1
hr per fortnight.

C. The erythemal UV to the shoulder of a person relaxing
in a sunroom in spring for 1 hr/day for 14 days per
fortnight compared to spring gardening of 1 hr per
fortnight.

For all three scenarios, the exposures to the shoulder of the
spectator, beach-goer and gardener were taken as the erythemal
exposure measured outside the enclosures on a horizontal plane
with the meter.

Results and Discussion

Filtered Irradiances

The erythemal exposures for the six hour periods to the
horizontal and vertical surfaces between 9.00 and 15.00 EST in a
glass enclosure, a greenhouse, a small car and a large car are
provided in Table 1. The unfiltered erythemal UV on a horizontal
plane over a six hour period measured outside each enclosure are
also provided. The erythemal exposures were converted to units of
a minimum erythemal dose (MED) where one MED is defined as 20 mJ
cm-2 (Diffey, 1992) and
is the amount of biologically effective UV required to produce
barely perceptible erythema after an interval of 8 to 24 hours
following exposure. The erythemal exposures, particularly, the
lower ones in the greenhouse and in the small and large cars are
too low to be measured with a Robertson-Berger meter. Whereas,
with the spectrum evaluator, the exposure time was lengthened for
these lower exposures to record the cumulative effect. For the
glass enclosure and greenhouse the exposures in the row called
vertical are the average of the exposures to the four vertical
orientations, namely, 0o, 90o, 180o
and 270o of azimuth angle from north and for the small
and large cars, the horizontal and vertical orientations are the
right hand and right upper arm sites respectively.

Table 1 The unfiltered solar erythemal UV on a horizontal
plane and the erythemal exposures due to filtered solar UV
radiation over a six hour period in a glass enclosure, a
greenhouse, a small car and a large car. For the small and large
cars, the horiz ontal and vertical orientations are the right
hand and right upper arm sites respectively.

Erythemal Exposures (MED) over a six hour
period

Glass Enclosure

Greenhouse

Small car

Large car

4 Sept 96

18 Oct 96

28 Nov 96

5 Feb 97

25 Aug 97

25 Aug 97

Ambient

11.6

18.1

18.7

22.4

10.5

10.5

Horizontal

0.85

0.89

0.25

0.25

0.13

(r. hand)

0.07

(r. hand)

Vertical

0.38

0.44

0.11

0.12

0.16

(r. up. arm)

0.07

(r. up. arm)

In order to compare the erythemal exposures in each
environment, the ratios of the filtered irradiances to the
erythemal irradiances measured outside the enclosures are
provided as a percentage in Table 2. Relative to irradiances
measured outside the environments, the inside of the glass
enclosure received the highest irradiances of the enclosures to
both the horizontal and vertical planes. The relative irradiances
to the right hand of the manikin in the small car were
approximately the same as those in a horizontal plane in the
greenhouse. In comparison, due to the manufacturer's window tint
on the large car, the right hand of the manikin in the small car
received approximately 1.7 times more than that in the large car.
The vertical surface of the right upper arm in the small car
received more than the exposure on the horizontal surface of the
right hand due to the proximity of the upper arm to the side
window glass. There is no difference between the two sites for
the large car, again as a result of the tint.

Table 2. Ratios expressed as a percent of the erythemal
irradiances inside each of the environments to those measured
outside the enclosures.

Filtered/Ambient (%)

Glass Enclosure

Greenhouse

Small car

Large car

Horizontal

5 - 7

1

1.2

0.7

Vertical

2 - 4

0.5 - 0.6

1.5

0.7

The average of the erythemal exposures measured at four sites
on the face of the manikins over the six hour exposure period in
the small and the large cars are in Table 3. For the small car,
the exposure to the face is reduced by a factor of 210 compared
to the ambient exposures outside on a horizontal plane. For the
large car, the exposures are reduced by a factor of 525.

Table 3. Erythemal exposures to the face.

Enclosure

Facial Exposure (MED)

Ambient (MED)

Small car

0.05

10.5

Large car

0.02

10.5

In Table 4, the erythemal exposures in each environment have
been employed to determine the time required to produce an
exposure of 1 MED for each environment. For the horizontal plane,
this is 6.7 to 7.1 hours for the glass enclosure compared to 24
hours for the greenhouse, 46 hours for the small car and 86 hours
for the large car. This difference is due predominantly to the
additional shading provided by the shadecloth on the top of the
greenhouse roof glass and by the protection provided by the top
of the cars and by the manufacturer's tinting on the window glass
of the large car.

Table 4. Time in hours required to produce an exposure of 1
MED in each of the enclosures.

Time (Hours)

Glass Enclosure

Greenhouse

Small car

Large car

4 Sept 96

18 Oct 96

28 Nov 96

5 Feb 97

25 Aug 97

25 Aug 97

Horizontal

7.1

6.7

24

24

46

86

Vertical

16

14

55

50

38

86

Typical Scenarios

The filtered and unfiltered exposures in Table 1 have been
employed to provide in Table 5 a comparison of the filtered
erythemal exposures received in three hypothetical scenarios. The
type of activities are listed in the second column and the fourth
column. The third column provides the result of the exposure due
to filtered radiation and the fifth column gives the result of
outdoor exposure. In scenario A, the exposures to the right upper
arm in the small car in winter were taken as an estimate of the
exposure to the right upper arm of a farmer in a tractor cabin
during winter. In a fortnight, the farmer received an exposure to
the right upper arm of the same order as that to the shoulder of
a spectator at a winter sport for 1 hr/fortnight. For each day in
the fortnight, the exposure to the shoulder of the worker in the
greenhouse in scenario B was taken as the average of the
exposures to the horizontal plane on both measurement dates for
the greenhouse in Table 1. The exposure to the shoulder of the
beach-goer was estimated as the average of the exposures on the
two dates to the horizontal plane outside the enclosure in Table
1. In a fortnight, the worker received an exposure of the same
order as that received to the shoulder in a summer beach visit of
1 hr/fortnight. In scenario C, the exposure in one hour each day
to the shoulder of a person relaxing in the sunroom was estimated
as one sixth of the average exposures on the two measurement
dates received in the six hour exposure in the glass enclosure in
Table 1. The exposure to the shoulder of the gardener was
estimated as the average of the exposures on the two dates to the
horizontal plane outside the enclosure. The person in the sunroom
received an exposure of the same order as that to the shoulder of
a person gardening in spring for 1 hr/fortnight.

Table 5. Comparison of erythemal UV exposure in different
scenarios.

Scenario

Activity in Protected Environment

UVBE
(MED)

Outdoor Activity

UVBE
(MED)

A.

Farmer in cabin of tractor - winter
(6 hr/day for 12 days/fn)

1.9

Spectator at winter sport
(1 hr/fn)

1.7

B.

Worker in greenhouse - summer
(6 hr/day for 12 days/fn)

3.0

Summer beach visit
(1 hr/fn)

3.4

C.

Relaxing in sunroom - spring
(1 hr/day for 14 days/fn)

2.0

Spring gardening
(1 hr/fn)

2.5

Conclusion

Although the level of UVB radiation can be reduced
substantially by various types of barriers such as plastic and
glass, UVA radiation can penetrate through these materials. As a
result, exposures to erythemal solar radiation can be incurred
under the protection of UVB barriers. On the measurement dates,
the inside of the glass enclosure received the largest amount of
erythemal UV radiation of the four environments. Relative to the
erythemal exposures outside the environments, the interior of the
glass encl osure on a horizontal plane received approximately 5
to 7 times more than the inside of the greenhouse, the exposure
to the right hand in the small car was of the same order to that
on a horizontal plane in the greenhouse and approximately 1.7
times more than the exposure to the right hand in the large car.

The cumulative exposure to filtered erythemal UV radiation
over a two week period to a farmer in a tractor cabin, a worker
in a greenhouse and a person relaxing in a glass sunroom were
respectively of the same order of magnitude as the cumulative
exposure to unfiltered erythemal UV radiation received in a one
hour period by a spectator at an outdoor sport, a person at the
beach and a gardener. The cumulative erythemal UV exposure
received over a period due to filtered solar radiation may be as
high as that received during periodic leisure activities. With
the publicity and education campaigns on sun exposure, the
general population may be more aware of the dangers of UV
radiation at the beach, at a sportsground or in the garden and
take appropriate protectiv e measures. However, the general
population may underestimate or not be aware of the erythemal UV
due to filtered UV received in an enclosure and as a result not
take any protective measures.